15 Reaction of Trimethylamine with Η AlBN •Ν(CΗ ) 2
JOHN
K. RUFF
Gorgas
Laboratory,
Downloaded by KTH ROYAL INST OF TECHNOLOGY on January 9, 2017 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch015
Huntsville,
Redstone
Arsenal
Research
Division,
4
Rohm
3 3
& Haas
Co.,
Ala.
The H AlBH ·N(CH ) complex absorbs one mole of N(CH ) to form Η ΑlΒΗ ·2N(CH ) . This material is not stable and disproportionates to ΑlΗ ·N(CH ) and ΒΗ ·N(CH ) . An equilib rium exists among these three species. P r e l i m inary results on the interaction of N(CH ) and HAl(BH ) ·N(CH ) are also reported. 2
4
3
3
3 3
4 2
3 3
3 3
3
2
3
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3 3
3 3
3 3
T he reaction of amines with the boron hydrides has been studied by many investigators and several reaction modes have been observed. Boron when bonded to bridging hydrogens was found to be susceptible to nucleophilic attack and symmetrical cleavage of diborane upon treat ment with tertiary amines occurred readily (1, 6) . On the other hand, the reaction of nucleophiles with aluminum borohydride has been little studied. The borohydride groups in aluminum borohydride are believed to be bonded to aluminum by two hydride bridges (2) and in this respect aluminum borohydride resembles diborane. The results of an early study (5) on the reaction of trimethylamine with A l (BH ) suggested that some symmetrical cleavage of the bridge bonds occurred. The system was found to be complicated and the presence of several species was indicated. However, more recently it was shown that treatment of HA 1BH N(CH ) and A1(BH ) N(CH ) with trimethyla mine resulted in a rapid quantitative cleavage of the hydride bridges according to the equations (3) : 4
4
(CH ) NA1(BH ) 3
2
4
3
2
4
+ 2N(CH )
2
3
(CH ) NA1(BH )H + N(CH ) 3
2
4
3
3
3
_> H A1N(CH ) 2
_>
3
2
3
H A1N(CH ) 2
3
2
2
+
3
2
2BH N(CH ) 3
3
+ B H N(CH ) 3
3
3
3
The reaction of trimethylamine with similar derivatives was ex tended to include H A l B . N(CH ) and the preliminary results of a study of the HA1(BH ) · N(CH ) -N(CH ) system were obtained. 2
4
4
2
3
3
3
3
3
Experimental Materials. The hydrido aluminum borohydride complexes were prepared as described (3). Trimethylamine was obtained from the Mathieson Co. and used after drying over lithium aluminum hydride and fractionating through a -64° bath. 139
Niedenzu; Boron-Nitrogen Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1964.
140
ADVANCES 2
4
3
3
3
2
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IN
C H E M I S T R Y SERIES
Reaction of H A1BH · N(CH ) with N ( C H ) . Sealed Bulb Experi ments. A 0.356-gram sample of H A1BH and 5 m l . of paraffin oil were placed in a 25-ml. pressure flask equipped with a F i s c h e r Porter Teflon needle valve. Trimethylamine (0.987 gram) was con densed into the flask, and the mixture was allowed to stand at 25° for 24 hours. Upon fractionation 0.564 gram of trimethylamine was r e covered. Sublimation of the residue at 0° produced 0.172 gram of trimethylamine-borone (m.p. 92-93°). After 6 hours the temperature of the residue was raised to 35° and the sublimation was continued. The next batch of sublimate collected over a 15-minute period con tained both B - H and A l - H materials (as evidenced by infrared). Finally a 0.101-gram sample of A1H ·2N(CH ) was isolated (m.p. 95-98°). Thus 2.07 moles of TMA were consumed per mole of boro hydride derivative. The procedure was repeated using 0. 321 gram of H A 1 B H - N ( C H ) , 0.879 gram of trimethylamine, and 5 ml. of tol uene instead of paraffin oil. After the excess TMA had been removed (0.501 gram was recovered), while the reaction flask was held at -45° a sample of the remaining solution was taken to obtain a B N M R spectrum. This consisted only of a quadruplet centered at 26.3 p . p . m . relative to methyl borate, J = 100 c./s. Tensometric Titrations. The procedure used has been described (4)- A solution of 0. 216 gram of H AIBI^. N(CH ) in 5 ml of rc-decane was treated with known amounts of trimethylamine. If only 15 minutes at 25° were allowed to establish equilibrium, curve a in Figure 1 was obtained. The titration was repeated using 0.196 gram of H BI^ · N(CH ) in 4 ml. of n-decane and 6 hours at 25° was allowed to establish equilibrium after each addition of amine. The second titration is shown in curve b of Figure 1. Reaction of HAl(BHj · N(CH ) with N(CH ) . Sealed Bulb Experi ments. The procedure followed is identical to that described above. A solution of 0.428 gram of ΗΑ1(ΒΙ^) · N(CH ) in 5 m l . of paraffin oil comsumed 0.632 gram of trimethylamine, and a 0.194-gram sample of BH -N(CH ) (m.p. 91- 92°) was obtained by fractionation. Similarly, a solution of 0.401 gram of H A l i B H ^ * N(CH ) in 5 m l . of toluene con sumed 0.592 gram of N(CH ) . A B NMR spectrum of this solution consisted of a quadruplet, δ =25.9 p . p . m . , J = 101 c./s. relative to methylborate. Small amounts of a noncondensable gas (shown to be hydrogen by mass spectral analysis) were present in these two runs. Tensometric Titrations. When the titration was performed at 25°, equilibrium was not attained and the pressure did not remain constant over a 15-minute period after addition of amine. However, when the titration was performed at 0°the pressure was constant over a 15-minute period after reaching thermal equilibrium and its value was recorded. A solution of 0.176 gram of HAliBHji, · N(CHg) in 4 m l . of w-decane gave an end point ratio of amine to hydride of 1.07. Because of the lower observed pressures, the break was not as sharp as those shown in F i g ure 1. Attempted Isolation of H A1BH · 2N(CH ) . A 0.401 -gram (3.89 mmole) sample of H A1BH · N(CH ) was placed in a weighed flask was 10 ml. of dried diethyl ether; then 3.82mmoles of trimethylamine were condensed into the flask. The flask was stirred 10 minutes at -78° and warmed to -35°. The ether was removed at this temperature under vacuum and the solid residue was dried under vacuum for 1 hour at -35°. 3
4
3
2
4
3
3
3
3
1 L
B
H
2
3
3
2
3
3
2
3
3
2
3
3
3
3
3
3
3
3
11
3
B
H
3
2
2
4
4
3
3
3
3
Niedenzu; Boron-Nitrogen Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1964.
15
RUFF
Trimethylamine
Reaction with Aluminum
Borohydride
141
The flask was warmed to 0°; the residue remained as a white solid without change for several hours. The flask was then quickly weighed and the weight of the residue was found to be 0.641 gram [Calculated for H A l B H ^ N i C H ^ » 0.632 gram]. The solid liquefied on standing at 25°for several minutes. Approximately 2 ml. of toluene were added to the flask and the solution was aged one day before obtaining its B N M R spectrum. A 0.625-gram (6.08 mmole) sample of H A1BH -N(CH3) was treated with 6.04 mmoles of trimethylamine in the above manner. After removal of the ether, the residue was allowed to age at ambient temperature for 24 hours. Sublimation at 0° yielded 0.096 gram of B H - N(CH ) , (m.p. 94°). Sublimation of the remaining material at higher temperatures (20° to 45°) produced liquids and wet solids which were obviously impure. NMR Studies. A l l the B NMR spectra were obtained on a Varian Model 4300B spectrometer operating at 12.8 megacycles. Trimethylborate in capillary tubes was used as a standard in every case and toluene as a solvent. Decomposition of H AIBI^ . 2N(CH ) . The B NMR spectrum of the sample described above consisted of a quadruplet (ô =26.0 J = 100) and a quintuplet (ô =56.6 Λ β Η ) · relative areas of the two were found to be BH /BH4 = 0.739. In another experiment 0.379 gram (3.68 mmoles) of H2 ΑΙΒΉ^ .N(CH ) in 1 m l . of toluene was placed in a bulb equipped with a NMR tube extension on one side. T r i methylamine (3.60 mmoles) was condensed into the reactor and allowed to mix at -78° . The bulb was warmed at 25° and a sample of the solu tion was poured into the NMR tube and the NMR spectrum was run. Only a quintuplet was present (δ = 56.4
